* Fixed a problem with wrong query results for partially covering keys in ROR-index_merge
 * ROR-intersection retrieval plan choice algorithm now uses less disk IO
   - and properly processes clustered PK range scans 
 * Fixed several minor range optimizer problems
 * Added more comments
 * Code cleanup


mysql-test/r/index_merge.result:
  New index_merge EXPLAIN output format changes
mysql-test/r/index_merge_innodb.result:
  New index_merge EXPLAIN output format changes
mysql-test/r/index_merge_ror.result:
  New index_merge EXPLAIN output format changes
  Added test for scans on keys that cover fields partially
  Fixed a minor ROR optimizer problem
mysql-test/r/index_merge_ror_cpk.result:
  More tests added
mysql-test/t/index_merge_ror.test:
  New index_merge EXPLAIN output format changes
  Added test for scans on keys that cover fields partially
  Fixed a minor ROR optimizer problem
mysql-test/t/index_merge_ror_cpk.test:
  More tests added
mysys/my_bitmap.c:
  Comments added, code cleanup
sql/opt_range.cc:
  Comments added, code cleanup
  Numerous fixes, see changeset description
sql/opt_range.h:
  Comments added, code cleanup
  New index_merge EXPLAIN output format related changes
sql/sql_select.cc:
  Comments added, code cleanup
  New index_merge EXPLAIN output